A large number of base station antenna installations have been necessary for the operation of cellular mobile telecommunication systems. Base station antenna arrangements have to be provided all over the area that is to be covered by the cellular communication system and how they are arranged among other things depends on the quality that is required and the geographical coverage, the distribution of mobile units etc. Since radio propagation depends very much on terrain and irregularities in the landscape and the cities the base station antenna arrangements have to be arranged more or less closely.
However, the installation of multiple antenna base stations has caused protests among others from an esthetical point of view both on the countryside and in the cities. Also, the construction of these antenna masts is expensive, e.g. because each antenna needs to be supplied with energy via a separate, expensive feeding cable.
The introduction of new base station antenna arrangements would be considerably facilitated if the infrastructure that already is in place could be better used. Today various examples of microstrip antenna elements which are capable of operating in two distinct frequency bands are known. However, it is difficult to avoid grating lobes when the frequency bands are not closely spaced.